1. Field of the Invention
The present invention relates to a nitride semiconductor device which uses a nitride semiconductor (InXAlYGa1−X−YN, 0≦X, 0≦Y, X+Y≦1) used in light emitting devices such as light emitting diode device (LED) and laser diode device (LD), light receiving devices such as solar cell and optical sensor or electronic devices such as transistor and power devices, and particularly to a nitride semiconductor device comprising a nitride semiconductor layer which includes In.
2. Description of the Prior Art
Recently semiconductor laser devices which use nitride semiconductors have been receiving increasing demands for the applications in optical disk systems such as DVD systems which are capable of recording and reproducing a large amount of information with a high density. Accordingly, vigorous research efforts are being made in the field of semiconductor laser devices which use nitride semiconductors. Because of the capability to oscillate and emit visible light over a broad spectrum ranging from ultraviolet to red, the nitride semiconductor laser device is expected to have wide applications, such as light sources for laser printers and optical networks, as well as the light sources for optical disk systems. The applicant of the present invention reported a laser which successfully underwent over ten thousand hours of operation under the conditions of continuous oscillation at a wavelength of 405 nm with output power of 5 mW at room temperature.
Light emitting devices and light receiving devices which use nitride semiconductors have a nitride semiconductor structure which includes In for the active layer and, accordingly, it is important to form a better active region in the active layer in order to improve device characteristics.
In the prior art, n-type nitride semiconductors doped with n-type impurities have been used for the active layer of the nitride semiconductor device. Particularly in the case of a quantum well structure device, n-type nitride semiconductors doped with n-type impurities have been used in the well layer and the barrier layer.
In order for light emitting devices which employ nitride semiconductors to have wide applications they must be further improved with respect to device characteristics, particularly in device lifetime.
It is essential to have a longer lifetime and a higher output power for the laser devices which use nitride semiconductors as light sources for reading or writing information in high-density optical disk systems, described above, and further applications. Other classes of nitride semiconductor devices are also required to have longer lifetimes and higher output power, and light emitting devices are required to have a higher output power of light emission.
Weak reverse withstanding voltage of the devices using nitride semiconductors has been a problem in the prior art, in that such devices have a high probability of destruction during handling in the manufacturing process and mounting on an end product.
The present invention has been made in consideration of the problems described above, and aims at obtaining a nitride semiconductor device which has excellent device characteristics including the threshold current density and has longer device lifetime and high output power.